1. FIELD OF THE INVENTION
The present invention relates to a novel chemiluminescent microemulsion which can be used as an analytic tool for the detection of oxidants in aqueous samples. In addition, the present invention relates to an analytic technique and analytic arrangement which uses peroxyoxalate chemiluminescence in a microemulsion to determine the approximate oxidant concentration of an aqueous sample.
2. DESCRIPTION OF THE PRIOR ART
The detection of the approximate concentration of pollutants or contaminants, particularly those which generate an oxidizing agent such as hydrogen peroxide, by chemiluminescent analysis is well known. The detection of peroxide has been reported using luminol chemiluminescent techniques by G. L. Kok, et al., Envir. Sci. Technol. 12, pp.1072-1076 (1978); DeChatelet, L. R. et al., J. Immunol, 129, pp.1589-1593 (1982); B. Descamps-Latscha, et al., Ann. Immunol.. 133, pp.349-364 (1982); and p De Sole, et al., Adv. Exp. Med. Biol., 141, pp.591-601 (1982). Also, lucigenin chemiluminescence analysis in micellar systems has been described by W. L. Hinze et al. Anal. Chem. 56, p.2180 (1984).
However, the reported methods have several drawbacks. They are not very sensitive or efficient for the detection of oxidants, particularly hydrogen peroxide. Another drawback is that these prior art reactions require operating at a very high pH which necessitates adding large quantities of a strong base. This increases the risks of introducing contaminants and interferents such as metal ions.
The overall process of the peroxyoxalate chemiluminescence system, first described by Edward A. Chandross, Tetrahedron Letters, No. 12, p.761, (1963) and disclosed in U.S. Pat. No. 4,053,430, consists essentially of the reaction of an oxalic acid ester with H.sub.2 O.sub.2 in the presence of a fluorescer compound to generate chemiluminescence. The reaction sequence can be described by the following three steps: (1) An oxalate derivative is oxidized by an oxidizing agent such as H.sub.2 O.sub.2 to form the putative dioxetanedione intermediate, (2) this intermediate breaks down and transfers its energy to a fluorescer also present in the system, (3) the fluorescer then emits a photon. This system is very efficient. Despite the system's broad use for illumination, the prior art methods have not been used in chemical analysis because of the insolubility and lability of the chemiluminescent reagents in aqueous medium.
G. Scott, W. R. Seitz and J. Ambrose, Anal. Chem. Acta, 115, p.221 (1980) report grave difficulties with attempts to find compatible solvents for quantifying aqueous H.sub.2 O.sub.2 in a peroxyoxalate chemiluminescent flow injection system. A. G. Mohan et al., "Aqueous Peroxyoxalate Chemiluminescence," AD121,396, Defense Technical Information Center, Cameron Station: Alexandria, Va. 22304-6145, p.16, (1982), describe the peroxyoxalate chemiluminescent reaction in a cyclohexane in water emulsion. They reported no significant improvements in results. In additional work, they reported that better results were obtained when a detergent was included.
In U.S. Pat. No. 4,647,532, Watanabe et al. describe a method for the detection of hydrogen peroxide using a chemiluminescent method. This method involves a complex, multistep reaction of a hydrogen peroxide component in the presence of an oxidizing catalyst to convert a nonfluorescer substance to a fluorescer substance and then reacting the fluorescer substance with an oxalic acid diester and hydrogen peroxide to produce light.
None of the above methods is efficient in producing chemiluminescence or for adapting chemiluminescence to analytic techniques. The most efficient fluorescent compounds useful in peroxyoxalate chemiluminescence, including rubrene, perylene, and bis-(phenylethynyl)anthracene, are all insoluble in water. The most efficient oxalate derivatives, including amides and esters, have strong electron withdrawing groups that favor hydrolysis in aqueous solution. This insolubility and lability of the oxalate derivatives and fluorescers in aqueous media or other protic solvents is a limiting factor for the successful use of peroxyoxalate chemiluminescence as a light source or in analytic chemistry.